A jury in the United States has this week been asked to decide if two leaders of a white supremacist prison gang deserve the death penalty after being convicted of murder and racketeering. But who are the Aryan Brotherhood and why do such gangs thrive in US jails?

Barry "The Baron" Mills is believed to be the gang's leader

In July, a California jury convicted four leaders of a white supremacist prison gang of murder, conspiracy and racketeering.

Barry "The Baron" Mills, Tyler "The Hulk" Bingham, Edgar "The Snail" Hevle and Christopher Overton Gibson had denied all the allegations against them.

The federal authorities claimed they helped turn the Aryan Brotherhood (AB) into one of the most violent and insidious gangs ever to operate inside US prisons.

In many US prisons the population is divided along racial lines. Inmates often join gangs such as the AB out of a desire for self-preservation.

Motivated by power

The AB was formed in the late 1960s partly in response to the formation of gangs like the DC Blacks and the Black Gangster Family.

US prison gangs

Aryan Brotherhood

Nazi Low Riders

Dirty White Boys

Black Gangster Family

Mandingo Warriors

Associacion Neta

Mexican Mafia (La Eme)

La Nuestra Familia

Los Hermanos de Pistoleros Latinos

It espoused white supremacy but many gang experts believe it was simply a flag of convenience for the AB, whose real motivation was power and wealth.

In recent years Mills, 58, and Bingham, 59, were two of the most important leaders of the AB. The third, "Big Al" Benton, became a prosecution witness and was given only a nine-year sentence for the murder of an inmate, Abdul Salaam.

Mills, Bingham and Hevle were convicted of the murder of Arva Lee Ray, an inmate at Lompoc penitentiary in California in 1989. But Mills and Bingham were acquitted of the 1993 murder, also in Lompoc, of William McKinney, an inmate who dared to leave the AB.

The trial was one of several which stemmed from an operation launched in October 2002 with a series of raids on inmates and their alleged accomplices in jails all over the United States.

Code system

The indictment named 40 people, including a prison guard, and accused them of involvement in murders - both inside and outside jails - extortion, robbery, and drug trafficking.

It was the largest federal capital case ever to come to court, with at least a dozen people facing the death penalty.

Every time these men made a choice, people died. At some point, somebody has to stand up and say 'That's enough'

Joey BlanchAssistant US Attorney

But Terry Rearick, an investigator who worked for Mills's defence team, said he believed the AB had ceased to be a power long before the 2002 raids.

He said the FBI had exaggerated their influence and told the BBC News website: "The AB was like a flashy, violent streak across the prison sky between about 1981 and 1989. They were responsible for a number of spectacular murders but the most recent murder on the indictment was 10 years ago."

It emerged during the trial that AB members, many of whom were locked up in so-called supermax high security prisons, communicated using invisible ink made of urine.

It was also claimed they employed a 400-year-old binary code system devised by Sir Francis Bacon, with notes being smuggled out by guards, hidden in mop handles or under rocks in recreation yards.

This week the trial reached the death penalty phase - a jury will now have to decide whether Mills and Bingham deserve to be executed.

Assistant US Attorney Joey Blanch told jurors: "Mills is a six-time, multi-murderer and if he'd had his way he would have been responsible for 12 murders. Prison sentences did nothing to deter him from his criminal behaviour.

"Every time these men made a choice, people died. At some point, somebody has to stand up and say 'That's enough'."

More trials

Opponents of the death penalty do not accept the prosecution's argument.

Zachary Katznelson, senior counsel with the London-based pressure group, Reprieve, told the BBC News website: "It is wrong and uncivilised for the state to take a life.

The trial heard that Mills ordered John Greschner (pictured) to kill another inmate

"Practical reasons also argue against the death penalty for these men. As death is the ultimate punishment, it comes with built-in appeals to make sure the rules are followed.

"Even if these men were sentenced to death, 10 or 20 years would pass before they were executed."

Even if they are spared the death penalty, Mills and Bingham face spending the rest of their lives in the ADX supermax jail in Florence, Colorado, alongside former AB leader Tommy Silverstein - who has been in solitary confinement for 23 years.

"The ADX is not a nice place. It's stuck out in the desert of southern Colorado, it's like something out of science fiction. Nobody knows you're there. You could be in a cell next to your best friend for 20 years and you wouldn't know he was there," said Mr Rearick.

There are several more trials still to come, with one scheduled for 2008, and it seems the Brotherhood is finished as a major power.